The present invention relates to a cylinder head for an air-compressing, self-igniting injection internal combustion engine comprising a substantially plate-shaped cylinder head bottom with adjoining walls of gas exchange ducts and of a secondary combustion chamber separated from each other on the coolant side and exhibiting on the combustion chamber side sealing seats for valves, arranged approximately in a common plane, in the orifices of the gas exchange ducts, wherein the secondary combustion chamber comprises a combustion port of a cross section smaller as compared with the chamber cross section and the combustion port is oriented approximately centrally toward a relatively wide main web extending between two inlet valves in the cylinder head bottom.
In a known diesel internal combustion engine of the aforementioned type, as disclosed in German Patent Application M No. 24807/Ia/46a.sup.2, for example, the cylinder head has a precombustion chamber centrally arranged with respect to the cylinder chamber. The precombustion chamber is connected to the cylinder chamber via an insert which has the same number of combustion ports as the number of valves arranged in the cylinder head bottom. The combustion ports are oriented between the valves in the cylinder head bottom to reduce the thermal stress on the valve disks.
In this known diesel-type internal combustion engine, three or two inlet valves and, respectively, three or two outlet valves are arranged about the cylinder axis within the cylinder projection upon the cylinder head bottom. This valve arrangement, intended for a high specific performance, however, does not make it possible, in conjunction with the central, relatively large-volume precombustion chamber, to achieve a sufficiently intense cooling of the webs between the valves. The webs are under additional thermal load due to the aforedescribed location of the combustion ports. The webs between the hot outlet valves as well as the webs between the hot outlet valves and the relatively cool inlet valves are under an especially high stress. In this system, considerable temperature differences occur at the valve seats, leading disadvantageously to a distortion or warping of the valve seats and the consequent reduced engine power or failure of the engine.
Finally, because the webs in the cylinder head bottom of this known cylinder head are arranged exclusively between the inlet valves and thus are relatively cool, an unfavorable temperature distribution results on the whole. This can result in cracks in the webs as well as in distortion of the valve seats and of the cylinder head bottom, with leakage of the valves and the cylinder head gasket.
German Pat. No. 938,159 discloses a liquid-cooled cylinder head with a turbulence chamber arranged essentially within the projection of the cylinder onto the planar cylinder head bottom. The turbulence chamber is oriented with its combustion port in such a way that the combustion port terminates in a web in the cylinder head bottom between an inlet valve, arranged in a countersunk fashion, and an outlet valve, arranged in a countersunk fashion. For the intense cooling of the web, the inlet and outlet ports constitute, with the outer wall of the turbulence chamber, approximately stellate-disposed ducts associated at the cylinder periphery in the cylinder block and in the cylinder head bottom with cooling water outlet bores. Baffle surfaces in the coolant chamber of the cylinder head are correlated with these outlet bores to achieve an especially efficient cooling effect. Besides the fact that the coolant chamber configuration is complicated from the viewpoint of casting technique, the intense cooling of the cylinder head bottom in the zone of the relatively cold inlet port as compared with the zone of the hot outlet valve as well as of the turbulence chamber leads also in this case to an adverse temperature distribution in the cylinder head bottom with the known disadvantages.
An object of the present invention is to provide a cylinder head of the aforementioned type which avoids these disadvantages associated with known cylinder heads. In particular, an object of the invention is to provide a cylinder head of the type referred to for an injection internal combustion engine wherein the hot zones existing around the outlet valve and the secondary combustion chamber in the cylinder head bottom, and the cold zones existing around inlet valves and/or ports are correleated with one another in such a way that a relatively uniform temperature distribution is attained in the cylinder head bottom.
These and other objects of the invention are attained by providing in a cylinder head of the aforementioned type that an outlet valve is arranged in the cylinder head bottom essentially diametrically opposite to an orifice of a single combustion port of the secondary combustion chamber.
The advantage of the invention resides in the separation of the greatly thermally stressed spots around the secondary combustion chamber and the outlet valve by interposed, intensively cooled zones around the inlet valves and/or ports, wherein the main web exposed to the combustion jet is arranged in the cold zone between the inlet valves. As a result, an extensively uniform temperature distribution is achieved in the cylinder head bottom, which latter exhibits a high fatigue strength even under a high thermal load exerted by engines of great specific performance under load.
DOS [German Unexamined Laid-Open Application] No. 2,139,500 does disclose a diesel-type internal combustion engine with two inlet valves and one outlet valve, but in this engine, equipped with direct injection, the series-disposed inlet valves are located at a parallel spacing from the plane of symmetry of the cylinder, due to the fact that the injection nozzle must be arranged approximately in the center of the cylinder, and the outlet valve is arranged diametrically with respect to an inlet valve asymmetrically to the inlet valves. In a multicylinder internal combustion engine, the outlet valve thus is disadvantageously close to the zone of the cylinder head notoriously critical on account of the drop in heat of the neighboring cylinder. This disadvantageous arrangement leads to warping of the cylinder head in the zone of neighboring cylinders, particularly in case of a high specific load, and therefore results in a permanent deformation with insufficient sealing between adjacent cylinders.
This disadvantage has been avoided by the present invention in that, according to a disclosed, preferred embodiment of the invention the cylinder head comprises two inlet valves arranged on respective sides of a first cylinder plane of symmetry and in an approximately contacting to overlapping fashion in regard to a second cylinder plane of symmetry located perpendicularly to the first, wherein the outlet valve and the orifice of the combustion port of the secondary combustion chamber on the cylinder side are arranged centrally in the first cylinder plane of symmetry, and wherein the outlet valve and the orifice are located respectively close to the periphery of a cylinder projection.
This construction achieves a relatively cool zone in a multicylinder internal combustion engine with a cylinder head integrally extending over all cylinders, in the region of the longitudinal line of symmetry thereof, by means of series-disposed inlet ports, wherein the hot spots of the secondary combustion chamber and of the outlet valve are located near the longitudinal sides of the cylinder head. Since in this case a not insubstantial proportion of the heat from each hot spot is carried away via the adjacent cylinder head side, the cylinder head remains relatively cool in its longitudinal line of symmetry area passing over the narrowest gasket sections between neighboring cylinders, and accordingly retains sufficient rigidity for a flawless seal between adjacent cylinders.
This arrangement of the invention furthermore has the advantage that the spacing between the combustion port and the outlet valve, arranged diametrically thereto, is advantageously large for a thermally lesser effect on the outlet valve.
According to a further feature of the invention the cylinder head bottom of the cylinder head is planar and has valve seat rings inserted therein, and respective secondary webs are formed between the valve seat rings of the inlet valves and the valve seat ring of the outlet valve and between the valve seat rings of the inlet valves and a burner insert of the secondary combustion chamber, the secondary webs having a width at their narrowest points of approximately half the width of the main web between the inlet valves. Thus, in the disclosed, preferred embodiment of the invention the diametrically located hot zones are separated from the interposed cold zone constituted by the inlet ports respectively by means of web portions of identical width. Since these web portions are furthermore connected to the main web, exposed to the combustion jet, between the inlet ports, a satisfactory heat distribution in the cylinder head bottom is attained via these secondary webs located away from the combustion jet.
The cylinder head of the invention is also characterized by a coolant chamber for liquid cooling as well as inlet ports and an outlet port extending separately from one another through the coolant chamber wherein the inlet ports terminate on one cylinder head side and the outlet port terminates on the opposite cylinder head side. The walls of the inlet ports in the coolant chamber are arranged, at least in the sections close to the cylinder head bottom, freely exposed all around in the coolant chamber and formed, with respective wall sections of the outlet port and the secondary combustion chamber ducts in the region of the inner surfaces of the secondary webs on the coolant side. The ducts are oriented toward the main web. The inlet ports are provided in the close proximity of the cylinder head bottom and are separated from each other as well as from the outlet port and from the combustion chamber wall. By the separated arrangement of the aformentioned components, they are, on the one hand, exposed to the coolant on all sides and, on the other hand, the cylinder head bottom is intensively cooled by way of the webs between the components. Thus, in the regions of the secondary webs on the coolant side, ducts having a radiating pattern are produced for the coolant by the arrangement of the aforementioned components in the coolant space, these ducts being oriented toward the main web. The ducts are aligned and dimensioned in such a way that the thermally highly stressed main web is intensively cooled by a coolant flowing longitudinally and/or transversely through the cylinder head. Since the cylinder head bottom is also exposed to coolant in the interstices of the outlet and inlet ports and the secondary combustion chamber, the wall thickness of the cylinder head bottom can be adapted better to the requirements in conformance with the amount of cooling obtained at maximum engine power. In this connection it is optically possible, by controlled differences in the wall thickness, to advantageously affect the temperature distribution.
Further, according to the present invention the cylinder head comprises a coolant chamber formed above the cylinder head bottom between the cylinder head sides and a cylinder head cover wall. The outlet port is arranged essentially freely exposed all around in the coolant chamber between the cylinder head bottom and the cylinder head cover wall and terminates in a cylinder head side. The inlet ports are freely exposed all around following the cylinder head bottom, ascend relatively steeply in the coolant chamber, and penetrate the cylinder head cover wall. The ascending inlet ports constitute with the adjacent cylinder head side a section of the coolant chamber. Formed recesses of the cylinder head bottom and of the cylinder head side are arranged freely exposed in the coolant chamber to accommodate the secondary combustion chamber and an insert bore of an injection nozzle. In this way the cylinder head bottom can be cooled intensively by an uninterrupted conductance of coolant and at the same time the cylinder head bottom is rigidified by means of the inlet ports penetrating the cylinder head cover wall and ascending relatively steeply in the coolant chamber.
In a multicylinder injection internal combustion engine with a continuously extending cylinder head, these inlet ports rigidify the cylinder head bottom in the zone of the longitudinal center line with respect to the cover wall and separate the coolant stream in the zone of each cylinder into two partial streams, in case of a cylinder head exposed to longitudinal throughflow. One partial stream is conducted by way of the outlet port which is provided substantially exposed all around in the coolant chamber between the cylinder head bottom and the cylinder head cover wall, whereas the second partial stream is conducted primarily via the secondary combustion chamber. Accordingly, a partial stream of coolant is guided over each hot spot, both partial streams flowing, in the region of the longitudinal line of symmetry of the cylinder head, around the inlet ports which are relatively cool due to the taken-in air. By means of this conductance of coolant, the intensive cooling of the main web is advantageously enhanced. Furthermore, the cylinder head remains rigid in the region of its longitudinal line of symmetry, on account of the intensive cooling, for a flawless sealing action in the zone of adjacent cylinders even at a high specific performance.
The intensive cooling of the cylinder head in the zone of the longitudinal line of symmetry is furthermore promoted according to the invention in that each hot spot is additionally exposed and/or surrounded to or by the coolant from the cylinder block by way of passage openings provided in the cylinder head bottom.
In particular, according to the invention the cylinder head is provided with screw holes between the cylinder head bottom and the cylinder head cover wall in the close proximity of the cylinder head sides. Coolant passages are formed in the cylinder head bottom, the coolant passage openings including a slot-hole-shaped coolant passage opening arranged in the zone of the outlet port between two screw holes and respective coolant passage openings arranged between the secondary combustion chamber and the two adjacent screw holes according to the disclosed, preferred embodiment of the invention.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, one preferred embodiment in accordance with the present invention.